Cyclin localization controls activity

Exiling a protein from the scene of the reaction is one way to manage its activity. Cells adopt this method to reign in the cyclins, proteins that orchestrate the cell cycle. By tracking two cyclins from one mitosis to the next, Tony Hunter of the Salk Institute for Biological Studies in San Diego, California, and his post-doc Jonathon Pines were the first to demonstrate the importance of subcellular location for the molecules.

Cyclins team up with proteins called cyclin-dependent kinases (Cdks) to organize different steps of cell division. Cyclins A and E prompt DNA replication, whereas cyclin B1 pushes the cell to advance from the G₂ phase to mitosis. In the early 1990s, Hunter recalls, researchers were debating whether the...